1. Field of the Invention
The invention relates to a method for heating a furnace comprising at least one burner capable of operating on an oxidant the oxygen content of which can vary. Such burners, described, for example, in documents EP-192,682 and EP-432,153, are designed for various situations.
2. Description of Related Art
Most industrial furnaces, such as (s)melting furnaces or annealing furnaces, are equipped with burners which operate on air as the oxidant.
In each application of these burners, a specific oxidant, for example consisting of oxygen-enriched air, is chosen, the oxygen content of the oxidant being kept constant during operation.
Document GB-A-1,514,842 describes a method in which oxygen is periodically added to the oxidizing air to smelt successive charges of scrap in a furnace; after this the oxygen supply is interrupted and the charge is refined using only air as the oxidant. This therefore is a conventional burner "doped" with oxygen in the flame, this document not envisaging the use of pure oxygen.
Document U.S. Pat. No. 4,931,013 teaches the use of a burner which is "doped" with a pure oxygen lance, the injection of which pure oxygen into the combustion air enriches its oxygen content to as much as 35%. Thus, in a first phase, hydrocarbons are completely burnt by virtue of this oxygen "doping", then the injection of pure oxygen is interrupted and the process continues using only oxygen-enriched air.
Patent abstracts of Japan Vol. 098 No 003 of 27.02.1998 (JP-09-30728) relates to a cremation method in which, in a first phase, a conventional burner is used; in a second phase, in order to be able to cremate items which are difficult to burn, use is also made of a lance which injects a mixture of air and oxygen onto these items on the outside of the burner.
In all these known methods, the air supply is never interrupted, and the oxygen content of the oxidant never exceeds 35%.
Now, depending on the furnaces and particular envisaged applications thereof, and on considerations relating to the thermal performance and running cost, it may prove advantageous to be able to alter the oxygen content in a range which is far wider than 21 to 35%. An oxygen content of 21% is that of air, an inexpensive oxidant but one whose thermal performance is modest. Conversely, an oxidant consisting of almost pure oxygen is very powerful, but expensive. Now, the known burners of the state of the art do not allow such relative optimization of performance with respect to economic cost.
The invention therefore sets out to propose an optimized and economic heating method for all applications of the burners in question.